[Truncated abstract] In this dissertation an investigation into the utility of mechanochemically synthesized nanopowders for intermediate temperature solid oxide fuel cell components is reported. The results are presented in the following parts: the synthesis and characterisation of precursors for ceramic and cermet components for the fuel cell; the physical and electrical characterisation of the electrolyte and electrodes; and the fabrication, operation and analysis of the resulting fuel cells. Samarium-doped (20 mol%) ceria (SDC) nanopowder was fabricated by the solid-state mechanochemical reaction between SmCl3 with NaOH and Ce(OH)4 in 85 vol% dilution with NaCl. A milling time of 4 hours and heat treatment for 2 hours at 700°C yielded a material with equivalent particle and crystallite sizes of 17 nm. The existence of a complete solid solution was affirmed by electron energy loss spectroscopy and x-ray diffraction analysis. Doped-ceria compacts were sintered for 4 hours at 1350°C forming ceramics of 88% theoretical density. The ionic conductivity in flowing air was 0.009 S/cm, superior to commercially supplied nanoscale SDC. Anode precursor composite NiO-SDC nanopowder was synthesized by milling Ni(OH)2 with the previously defined SDC formulation ... Anode-supported fuel cells were fabricated on a substrate of at least 500 'm 55wt%NiO-SDC with 17vol% graphite pore formers. Suspensions of SDC were deposited by aerosol on the sintered bilayer at a thickness around 5 'm. A cathode of 10% SDC (SmSr)0.5CoO3 was deposited onto the sintered electrolyte and after firing had a thickness of around 25 'm. Operation of fuel cells in single-chamber mixtures of CH4 and air diluted in argon were successful and gave power outputs of 483 'W/cm2. Operation in undiluted 25 vol% CH4:air gave a power output of 5.5 mW/cm2. It was shown that a large polarisation resistance of 4.1 Ω.cm2 existed and this was assigned to losses in the anode, namely mass transport limitation associated with the catalytic combustion of methane and insufficient porosity. The large surface area of Ni appeared to allow more methane to combust and hence prevented its electrochemical reaction from occurring, thus limiting the performance of the cell. The synthesis procedures, ceramic processing and fabrication techniques and testing methods are discussed and contribute significant understanding to the fields of ceramic science and fuel cell technology.
| Identifer | oai:union.ndltd.org:ADTP/221185 |
| Date | January 2005 |
| Creators | Hos, James Pieter |
| Publisher | University of Western Australia. School of Mechanical Engineering |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | Copyright James Pieter Hos, http://www.itpo.uwa.edu.au/UWA-Computer-And-Software-Use-Regulations.html |
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